Posted
by
Soulskill
on Friday June 07, 2013 @09:29AM
from the microscopes-are-for-squares dept.

sciencehabit writes "The mushroom clouds produced by more than 500 nuclear bomb tests during the Cold War may have had a silver lining, after all. More than 50 years later, scientists have found a way to use radioactive carbon isotopes released into the atmosphere by nuclear testing to settle a long-standing debate in neuroscience: Does the adult human brain produce new neurons? After working to hone their technique for more than a decade, the researchers report that a small region of the human brain involved in memory makes new neurons throughout our lives — a continuous process of self-renewal that may aid learning."

According to TFA, the research which originally showed this could not be repeated since the chemical given to trace growth was found to be poisonous. Therefore it was based on a probably correct but unrepeatable experiment, something people in the hard sciences do not like. This new experiment has provided confirmation of the earlier result by a different method.

Actually I posted too fast. I went back and looked at what I read (just a few nights ago, by chance), and the book does not include the new result. It just said that the isotope ratios observed in the brain confirm the conventional view that neurons aren't being created. TFA reports that a small region of the brain has been found that does not conform to the conventional view.

Well ya see, Norm, it's like this. A herd of buffalo can only move as fast as the slowest buffalo. And when the herd is hunted, it is the slowest and weakest ones at the back that are killed first. This natural selection is good for the herd as a whole, because the general speed and health of the whole group keeps improving by the regular killing of the weakest members.

In much the same way, the human brain can only operate as fast as the slowest brain cells. Excessive intake of alcohol, as we know, kills brain cells. But naturally, it attacks the slowest and weakest brain cells first. In this way, regular consumption of beer eliminates the weaker brain cells, making the brain a faster and more efficient machine! That's why you always feel smarter after a few beers.

For those that don't know, Cliff Clavin was a character on the TV sitcom "Cheers".

It's been known since at least the '60s that brain cells regenerate, the question was whether that applied to the grey matter or just the glial cells.

And AFAIK, it's been accepted for years that neurogenesis applies to grey cells. Arguing that it doesn't apply would require one to have an alternate explanation for why and how memory and learning occur after the brain supposedly doesn't create new neurons. Or how precisely all that development happens in the brain after birth.

Arguing that it doesn't apply would require one to have an alternate explanation for why and how memory and learning occur after the brain supposedly doesn't create new neurons.

I was under the impression that the standard explanation was that learning and memory were based on connections, not generation of new cells.

Your impression is correct. You are born with (almost) all the neurons you will ever have. The density of synapses in your brain increases until you are ~18-20, then decreases somewhat and stabilizes. But the strength of the signal transmitted at any given synapse is subject to change at any time in your life, and is thought to be the mechanism for learning.

And AFAIK, it's been accepted for years that neurogenesis applies to grey cells.

Exactly. You'd have to be totally ignorant of at least the last decade of research in neuroscience to deny they regenerate. So I expect that the so-called "debate" was not among neuroscientists, but between people outside the field who insisted on clinging to outdated unfounded dogma, and those who had at least a single fucking clue.

The majority of the development of the brain after birth is myelination and growth of axons, not new neurons.

Axons, and dendrites.......

Given that more about the brain is unknown than known, it's dangerous to say that the majority of brain development is anything.

Storing memories might not be adequately explained by existing neurons growing and reconfiguring existing connections, because we still don't know what the brain is doing. We don't know how to take what we think it's doing and turn that into a Turing machine, for example.

For all we know there is some magic fairy dust in the brain that we haven't di

If only the Intelligent Designer had used the waterfall method and left behind requirements specs, functional specs, architecture specs, and design specs.

Unfortunately, based on results, it seems she used agile and we get random bits of this and that from whatever hare brained idea someone came up with at each morning standup and don't even have a documentation trail to help us figure out the black box.

The brain culls more connections than it makes during childhood and adolescence. But long range axons do increase in calibre, which takes up space and accounts for some of the growth of the brain. It probably accounts for some of the behavioural development as well because bigger axons carry signals long distances more effectively (even more so when they're myelinated).

Very little is known about the functional development, as it relates to the physical development, but we know quite a bit about both behav

. That doesn't mean that's all that's going on, but there doesn't have to be something else happening. The poster I replied to said that obviously the brain is growing new neurons because it develops after birth and we're able to learn.

Two things. First, it's one thing to be "accepted" that it happens, and totally another to prove that it happens. Secondly, this experiment allowed them to trace how much it happened, which wasn't really known before, and allows you to say much more about how much of a role neurogenesis plays in the adult brain.

It doesn't sound to me like nuclear weapon research had anything to do with this. If the link between nuclear research and this has anything to do with carbon-14 vs. carbon-12 then you can link this "brain discovery" to nearly any branch of research using carbon-14 dating...

It doesn't sound to me like nuclear weapon research had anything to do with this. If the link between nuclear research and this has anything to do with carbon-14 vs. carbon-12 then you can link this "brain discovery" to nearly any branch of research using carbon-14 dating...

It has nothing to do with carbon dating. As the A/C partially explains in another reply, the nuclear testing during the middle of last century increased the relative amount of C-14 in the environment, but it has been falling off since the test ban treaty went into effect in 1963.

Cells consist of lots of carbon, so *new* cells will be built out of whatever is available in the environment. Thus cells created before 1945 will have the "standard" ratio of C-12 and C-14, those created in the 1950s will have an increased proportion of C-14, and those created since 1963 will also have an increased proportion, though that increase has gotten smaller every year as the excess C-14 disappears from the environment.

So for cells created in the past ~100 years you can distinguish the pre-nuclear-testing ones from the later ones, and for cells created since 1963 you can give an approximate date based on the isotope ratio, since that ratio has been decreasing on a well-known curve.

People born before 1945 have the "standard" ratio of isotopes in most of the neurons in the brain, ergo those cells were created before 1945. People born more recently have an elevated ratio in most of the neurons in their brain, depending on what year they were born.

If new neurons were regularly created throughout life, people born before 1945 would also have an elevated ratio of the isotopes.

The news in TFA is that someone found a brain region with an elevated C-14 ratio in people born before nuclear testing started, and thus conclude that that region of the brain creates new cells later in life.

Cells consist of lots of carbon, so *new* cells will be built out of whatever is available in the environment. Thus cells created before 1945 will have the "standard" ratio of C-12 and C-14, those created in the 1950s will have an increased proportion of C-14, and those created since 1963 will also have an increased proportion, though that increase has gotten smaller every year as the excess C-14 disappears from the environment.

So for cells created in the past ~100 years you can distinguish the pre-nuclear-testing ones from the later ones, and for cells created since 1963 you can give an approximate date based on the isotope ratio, since that ratio has been decreasing on a well-known curve.

Oh, so it has absolutely everything to do with carbon dating, only that instead of using the ratio of C-12 and C14 to estimate the age of the sample directly, they use it to identify if the neurons' age match the patient's age (i.e., estimate the age of the neurons in a slightly more indirect way).

It will be so easy to date from the poisonous chemicals and radiactivity, You figure up to a century earlier we didnt have all these chemicals. And a more than a century hence we will have finished cleaning up our pigsty.

But I really think we could have done this more cheaply, more ethically, and more humanely through a controlled experiment. Call me jaded, but I have absolutely no romantic feelings of nostalgia towards the cold war. It was a time when the timeless "mine is bigger than yours" human defect almost destroyed human civilization.

My very elderly Canadian neighbour, at one time associated with Cold Spring Harbor Laboratory and retired from teaching at an American medical school more than 15 years ago, told me that a scientist at her university came up with photo micrographic evidence of of adult mammalian neurogenesis in the late 1940s. This caused some eye rolling and denial of tenure for heresy, and the fellow eventually disappeared. It had to wait 'til the sixties to be rediscovered by Altman.